The present invention relates to focus detecting devices for cameras. More particularly, the invention relates to a device for detecting the contrast of an image formed by a photographing lens to detect focalization.
It has been known in the art that the relation between the amount of non-focalization, specifically, the distance between the plane of an image at the point of focalization and the plane of an image at the point of non-focalization and the amount of high frequency components of the spatial frequency spectrum of an image can be represented by a symmetrical characteristic curve having a single peak as shown in FIG. 1. Accordingly, as the amount of non-focalization increases the amount of high frequency component decreases.
A technique for detecting the amount of high frequency components has been known in which an array of light receiving elements having uniform photoelectric characteristic and arranged along a straight line is disposed in a plane parallel to the plane of an image. In this arrangement, the amount of high frequency components is detected from the sum of the differences in output between adjacent light receiving elements. For convenience for the description, which follows the amount of high frequency components thus determined will be referred to hereinafter as "a contrast output".